An extended heat warning has been issued for Toronto after four days of scorching temperatures, with cooling stations open around the city. 

Environment Canada is predicting a high of 31 C with a humidex of 40 C on Monday.

Dr. Eileen de Villa, Toronto's Medical Officer of Health, issued a statement on Monday encouraging Toronto residents to visit air-conditioned buildings and check in on vulnerable family and friends to ensure they are keeping cool. 

Toronto cooling centre sign

Seven cooling centres now open in the city provide air-conditioned spaces for Torontonians to rest. (Kate McGillivray/CBC)

The heat is expected to continue into the early part of the week, with a high of 31 C expected again on Tuesday and a high of 29 C on Wednesday.

"A ridge of high pressure is anchored in the lower Great Lakes and it's going to continue for the next couple of days," Environment Canada meteorologist Yoseph Mengesha said Monday.

Air quality possible concern

Environment Canada advises people to schedule outdoor activities in the coolest parts of the day, to seek shade while outside and to keep cool in air-conditioned buildings.

"Especially for kids and elderly people... this will be very difficult," said Mengesha. "They have to stay hydrated and avoid strenuous outdoor activity." 

A list of cooling stations, where Torontonians can rest in an air-conditioned space and receive a cool drink and snack, can be found here

Air quality is also a potential concern, with Environment Canada's Air Quality Health Index indicating a "moderate risk" level.

The weather should begin to cool off by Thursday, with temperatures expected to go down to 21 C on that day and 17 C on Friday.

Many schools without air conditioning

The Toronto District School Board says that until temperatures cool off, teachers are doing what they can to keep students comfortable, including closing blinds, using fans, avoiding strenuous activity and moving students to the coolest parts of the school.

TDSB spokesperson Ryan Bird said 125 out of 584 TDSB schools are fully air conditioned and the cost of installing air conditioning at the remaining schools "would reach into the hundreds of millions of dollars." 

"The installation of full air conditioning at all remaining schools is not financially possible, however the TDSB is in the process of creating cooling stations at the remaining schools," he wrote to CBC Toronto in an email. 

"The plan, expected to take approximately 5 to 7 years, would cool large areas such as gyms or libraries." 

Ontario's Education Minister Mitizie Hunter said Monday that her government has provided $1.4 billion for school boards to make investments in renewal programs. 

"School boards can choose to prioritize air conditioning," she said. 

GO Trains were delayed

Meanwhile, commuters travelling toward Guildwood GO station faced delays up to 30 minutes on Monday morning after the hot weather delayed weekend track work at the Rouge Hill station.

On its website, GO Transit said that "as extra buses become available, we will run more trips for GO bus routes 92 and 96."

GO also advised that affected passengers could use their fare to board at several TTC stations including Union, Main Street, Yorkdale, York Mills, Scarborough Town Centre and Finch.